1. Field of Invention
The present invention relates generally to a diagnostic method of monitoring skeletal defects using low energy pulsed ultrasound. More particularly, the present invention relates to a novel method of separating the effects of soft tissues from those of hard tissues (for example, bone, tendons, cartilage or implanted material) on ultrasound propagation by using correlation analysis and spectral estimation, and by relating the velocity of the propagated ultrasound with the in vivo mechanical strength and structural integrity of hard tissues and in particular of load carrying hard tissues.
Management of patients with bone fractures is currently based on subjective impressions gained by physical examinations and x-ray radiographs taken during various stages of healing. Similarly, patients with bone diseases such as osteoporosis or those with microfractures are apt to be diagnosed solely on subjective impressions in the early stages, due to the limitations of standard radiographic techniques. Even after making a diagnosis based on experience, a physician will generally have to manage a patient conservatively before returning the patient to normal activity. The main reason for the delayed diagnosis in such bone disorders is that currently available diagnostic methods do not objectively access the mechanical strength and structural integrity of hard tissue such as bone, and thus do not provide any substantive failure risk analysis.
2. Description of the Related Art
Two general diagnostic methods are used to diagnose bone disorders. A first method employs ionizing radiation that essentially measures bone mineral density. This first method includes conventional and substrative x-ray imaging, single and dual photon absorptiometry, radio nuclide imaging, and CAT scans. While this first general method of diagnostic method has proven satisfactory for many uses, it has some inherent disadvantages. First repeated and/or excessive exposure to ionizing radiation is harmful to health and causes various kinds of cancer. Accordingly, a diagnostic method based on ionizing radiation cannot be used for frequent applications such as screening, especially of woman of child bearing age. Second, methods such as these are only sensitive to mineral density changes and not to the mechanical strength of hard tissues. Consequently such diagnostic methods generally do not provide information indicating when a bone is at risk of fracture. Third, the cost of diagnostic systems employing such methods significantly increases with the sophistication of the method. This causes economic burden on patients and limits their access to treatment.
The second general method of diagnostic method utilizes some sort of mechanical input to the bone and analyzes the response of the hard tissues. Depending on the kind of mechanical input, this second method can be generally categorized as an impact method, a conventional ultrasound method, or an acoustic emission method. This method of diagnostic system has definite advantages over ionizing radiation based methods because it provides direct information about the mechanical properties of bone, without harmful side effects. However, wide acceptance and clinical usage has not yet occurred. Two drawbacks contributing to the lack of wide clinical usage are the difficulty in controlling the input (e.g. ultrasound) and distortions in the received responses. These difficulties arise due to the effects of adjacent bones, muscles, ligaments and associated soft tissues on input to the bone and the reception of responses. In addition, this method, prior to the present invention, does not solve the problem of soft tissue effect on responses.
It is believed that the present invention will serve as a valuable adjunct to the diagnostic methods currently available and will probably shorten or prevent the disability of many patients. Further, this invention will provide valuable information about the efficacy of various methods of treating particular fractures and provide early diagnosis of bone diseases.